Conventional amplifier circuits often implement operational amplifiers. Supply voltages tend to decrease as process technology scales down. In low voltage applications, signal levels remain the same to obtain a targeted signal-to-noise ratio. Conventional input differential transistor pairs cannot satisfy stringent signal-to-noise specifications. Conventional approaches suffer from drawbacks such as low DC gain when input common mode is close to ground.
It would be desirable to implement a low-voltage constant-gm rail-to-rail CMOS stage with improved gain. It would also be desirable to implement a low voltage constant-gm rail-to-rail CMOS input stage that may be used in analog and/or mixed signal applications.